Device and method for mechanically locating and reading the setting of an adjustable valve

ABSTRACT

A device for mechanically locating and reading the setting of an adjustable magnetic valve for controlling the flow of a fluid in a predetermined direction (D) comprises a magnetic compass ( 10 ) and a selector ( 20 ) provided with an alignment mark ( 21 ) for aligning the magnetic compass ( 10 ) with respect to the direction (D) in which the fluid flows through the valve (V). The compass ( 10 ) comprises a reference plane and a magnetic indicator ( 12 ) which is mounted such that it can pivot in all three dimensions of space under the effect of the magnetic field of the valve, the valve setting being represented by the angle (β) formed, in the reference plane, between the magnetic indicator ( 12 ) and the alignment mark ( 21 ) when the magnetic indicator ( 12 ) is positioned perpendicular to the reference plane, the magnetic compass then being centered on the magnetic center of the valve.

The invention relates to a device and a method for locating andindicating the setting of an adjustable valve.

This type of valve is used in the field of medicine, for example, in thetreatment of hydrocephalus.

This affliction is characterized by hypersecretion of cerebro-spinalfluid (CSF), insufficient resorption, or a mechanical obstruction of thepassageways, thus leading to neurological and/or motor disorders in thepatient.

This type of valve is well known to those skilled in the art who can, inparticular, make reference to Patents EP 0 060 369 and EP 0 688 575 forexamples of embodiments of such a valve.

One of the technical problems that this valve is able to solve is thatof non-invasive adjustment of the valve setting. Indeed, while it isnecessary to operate on the patient in order to implant drainageapparatus including the valve and catheters at the required location, itis important for the settings to be able to be adjusted after theoperation in response to a positive or negative change in the disorderin order to drain more or less CSF from the cerebral ventricles or fromthe arachnoid space (cavum subarachnoidale).

In order to solve this problem, the valve settings can be adjusted byrotating a rotor equipped with magnetic elements. Usingsetting-adjustment apparatus also equipped with magnetic elements, it ispossible to rotate the valve, through the patient's skin, using themagnetic coupling between the magnetic elements of the valve rotor andthose of the setting-adjusting apparatus.

A first system of the prior art comprises an instrument for locating, aninstrument for indicating the setting and an instrument for adjustingthe setting of a valve implanted in a patient. These instruments areused in sequence. The location instrument is positioned over the valveonce this valve has been found by palpating the patient's skin. Thelocation instrument is then positioned on the skin over the valve sothat the valve sits in an aperture of the location instrument. Finally,the instrument for indicating the setting of the valve is positionedover the centre of the valve thus identified. This second instrumentcomprises a magnetized needle able to pivot in a plane. This needletherefore follows the orientation of the magnetic elements of the valveand therefore indicates the setting. The third instrument, the one foradjusting the setting, is in turn positioned over the valve andmanipulated in such a way as to allow a greater or lesser amount of CSFto pass. This device is not very practical because it is possible toconfuse the valve with a subcutaneous reservoir or with a bony outgrowthwithout the location instrument flagging this error, the needleorientating itself along the earth's magnetic field in the absence ofany other magnetic field. Furthermore, it is not very accurate becausethe aperture in the location instrument has, of necessity, to havedimensions large enough not to stretch the patient's skin to a dangerousextent that could injure it. Thus, the centre of the valve is identifiedonly approximately which means that errors may arise in the reading ofthe setting. Finally, as the centre of the valve is identified only byinserting the valve in the aperture of the location instrument, it isnot possible to locate then adjust the setting of a valve that isinaccessible or has been inserted more deeply.

Another system in the prior art consists of an indicator of the positionand of the setting of a valve implanted in a patient, comprising acompass that allows the valve setting to be determined. This compasscomprises an array of magnetic sensors and a signal processing devicefor processing the signal emitted by these sensors. These sensorsmeasure the field strengths in order directly to detect the setting ofthe valve without going through a step of determining the magneticcentre, which step is needless in the type of valve depicted in thispatent. Although it is accurate, this device is complicated to usebecause it entails computerized processing of the signal, andconsequently, a source of electrical energy.

In order to remedy the disadvantages of the known solutions, the presentinvention proposes, using a magnetic indicator that can be positionedwith respect to a reference plane, to identify the magnetic centre andthe orientation of the valve in this reference plane when the device issuperimposed on the valve.

To these ends, the subject of the invention is a device for mechanicallylocating and reading the setting of an adjustable magnetic valve forcontrolling the flow of a fluid in a predetermined direction, comprisinga magnetic compass and a selector provided with an alignment mark foraligning the magnetic compass with respect to the direction in which thefluid flows through the valve, in which device the magnetic compasscomprises a reference plane and a magnetic indicator which is mountedsuch that it can pivot in all three dimensions of space under the effectof the magnetic field of the valve, the valve setting being representedby the angle formed, in the reference plane, between the magneticindicator and the alignment mark when the magnetic indicator ispositioned perpendicular to the reference plane, the magnetic compassthen being centred on the magnetic centre of the valve.

This device thus makes it possible, in a single step, to locate, withaccuracy, the magnetic centre of the valve, determined by the positionof the magnetic indicator perpendicular to the reference plane, and toidentify the setting of the valve, as determined by the angular positionof the magnetic indicator with respect to the direction indicated by thealignment mark.

According to other embodiments:

-   -   the magnetic compass may have a detection means designed to        determine whether the axis of the magnetic indicator is        perpendicular to the reference plane;    -   the control means may be a centering sight;    -   the magnetic indicator may be designed to rest on a pivot        allowing it to rotate in all three dimensions of space under the        effect of the magnetic field of the valve;    -   the magnetic indicator may have a pin surmounted by a        setting-indicating element running substantially perpendicular        to the pin, a part for resting on the pivot and a part for        attaching at least one magnet able to receive a magnetic field;    -   the attaching part may be disposed on the opposite side of the        resting part to the setting-indicating element;    -   the magnetic indicator may comprise a pivot-angle restrictor;    -   the pivot-angle restrictor may be in the form of a        hemispherical, hemiovoid or frustoconical swivel cage;    -   a reinforcing means may be positioned in the resting part for        the pivot;    -   the reinforcing means may be made of a material chosen from        ruby, corundum and a ceramic;    -   a balancing ring may be positioned around the part for attaching        the magnet coaxial with the pin and on the opposite side of the        part for resting on the pivot to the setting-indicating element;    -   the device may further comprise magnetic screening intended to        protect the magnetic compass from an external magnetic field        other than that of the valve;    -   the selector and the magnetic compass may be separable; and/or    -   the selector may be equipped with a reading interface for        reading the setting of the valve (V).

The invention also relates to an assembly for locating and indicatingthe setting of a magnetic valve, comprising a device as above togetherwith a programmer able to emit a magnetic field strong enough to alterthe setting of the valve.

The invention also relates to a method for mechanically locating andreading the setting of an adjustable magnetic valve for controlling theflow of a fluid with a device for indicating the setting of a valve asabove, the method involving the steps consisting in:

-   -   a) orientating the selector in such a way that the alignment        mark is aligned with the predetermined direction in which the        fluid flows through the valve;    -   b) moving the said device over the valve, maintaining the        alignment with respect to the direction in which the fluid flows        through the valve,    -   c) immobilizing the said device when the magnetic indicator is        positioned substantially perpendicular to the reference plane,        then    -   d) identifying the angle formed, in the reference plane, between        the magnetic indicator and the direction indicated by the        alignment mark.

According to some other embodiments:

-   -   the method may further comprise a step e) which consists in        reading on a reading interface a pressure value corresponding to        the angle identified in step d);    -   the method may further comprise a step f) which consists in        using an assembly as above, in replacing the magnetic compass        with the programmer and in emitting a magnetic field strong        enough to alter the setting of the valve; and/or    -   the method may further comprise a preliminary step which        consists in initially locating the valve by palpation in an        approximate region in which the valve is located.

Throughout this text, the centre of the valve must be understood to bethe magnetic centre of the valve rather than its geometric centre.

The present invention can be used in any industrial or medicalapplication in which an adjustable magnetic valve, intended to controlthe flow of a fluid, has been installed or implanted with a knowndirection in which the fluid flows, but in a way that is not directlyaccessible, for example under a panel that it is difficult to remove, orin the body of a patient. Only the latter medical application of theinvention is described hereinafter, without this in any way meaning thatthe applicant is renouncing its rights in respect of industrialapplications.

Other features of the invention will be listed in the detaileddescription given hereinbelow with reference to the attached drawingswhich, respectively, depict:

FIG. 1: a schematic perspective view of a device according to theinvention for locating and indicating the setting of anadjustable-pressure magnetic valve,

FIG. 2: an exploded perspective view of the magnetic compass of thedevice of FIG. 1;

FIG. 3: an exploded perspective view of the magnetic indicator of themagnetic compass of FIG. 2;

FIGS. 4 and 5: schematic sectioned views of the magnetic compass of FIG.1, in use;

FIG. 6: an exploded perspective view of another embodiment of a magneticindicator according to the invention;

FIG. 7: an exploded perspective view of a magnetic compass incorporatingthe magnetic indicator of FIG. 6;

FIG. 8: a schematic sectioned view of the magnetic compass of FIG. 7;

FIG. 9: an exploded perspective view of another embodiment of a magneticindicator according to the invention; and

FIG. 10: a schematic sectioned view of a magnetic compass equipped withthe magnetic indicator of FIG. 9.

With reference to FIG. 1, a locating and setting-indicating device 100according to the invention comprises a magnetic compass 10, and aselector 20 equipped with a reading interface 22 and with an alignmentmark 21 for aligning the magnetic compass 10 with respect to thedirection D in which the fluid flows through the valve. This direction Dis known and predetermined at the time of implanting the valve (notdepicted) in a patient. As will be specified hereinafter, it ispreferable for the magnetic compass and the selector to be separablefrom one another so that a valve programmer can be fitted onto theselector in place of the magnetic compass once the magnetic centre hasbeen identified and thus be used to adjust the valve setting because theprogrammer is located precisely over the centre of the valve.

More particularly, the magnetic compass 10 comprises a plate 11preferably positioned parallel to a reference plane Pr (see FIG. 4) anda magnetic indicator 12 mounted in such a way that it can pivot in allthree dimensions in space under the effect of a magnetic field.

In a first embodiment of such a magnetic compass, as illustrated by theexploded view in FIG. 2, the magnetic compass comprises a transparentdome 13 in the shape of a hemisphere and a baseplate 14 which areintended, together, to form a housing with a flat lower base 14 a. Theattached plate 11 is intended to be fixed to the baseplate 14 in orparallel to a reference plane Pr, and the magnetic indicator 12comprises a setting-indicating element consisting of a needle 12 a andof a pin 12 b which is intended to be fixed perpendicular to the needle12 a.

In addition, the baseplate 14 is equipped with a pivot 15 the free endof which constitutes a point on which the pin 12 b can rest, so that itcan thus pivot in all three dimensions in space under the effect of amagnetic field.

FIG. 3 illustrates, in detail, the structure of the magnetic indicator12. In this embodiment, the magnetic indicator 12 can be dismantled andis made up of several components.

Thus, the pin 12 b comprises a means 12 c of attachment to the needle 12a so that this needle surmounts the pin 12 b, running substantiallyperpendicular to it.

The magnetic indicator 12 also comprises a part 12 d for resting on thepivot 15, this part being situated on a component 12 e intended to beattached to the pin 12 b.

This resting part 12 d is in the form of a frustoconical swivel cageallowing the pin 12 b to pivot in space without becoming detached fromthe pivot 15. This shape can also limit the three-dimensional rotationof the magnetic indicator to an extent that is dependent on its coneangle.

Furthermore, the magnetic indicator 12 is equipped with a part 12 f forthe attachment of an annular magnet 16, this attachment also beingsituated on the component 12 e. The attachment part 12 f is disposedopposite the needle 12 a with respect to the part 12 d for resting, thatis to say that it is on the opposite side of the pivot point to theneedle.

Finally, a reinforcing means 17 is positioned in the bottom of theresting part 12 d between the pin 12 b and the pivot 15.

The purpose of this reinforcing means is to reinforce the pivot point,and therefore achieve highly accurate pivoting. It may be made of acomponent made of ruby, corundum, ceramic, etc. positioned in the bottomof the resting part 12 d.

Upon assembly, the pin 12 b is fed through an opening 11 a in the plate11, then the needle 12 a is attached to the pin 12 b via the attachmentmeans 12 c. The magnetic indicator is then placed on the pivot 15 andthe plate 11 is positioned on the baseplate 14. Finally, the transparentdome 13 is attached to the baseplate.

The magnetic indicator 12 therefore rests on the pivot 15, allowing itto pivot in all three dimensions in space under the effect of a magneticfield. All that is then required is to choose an opening 11 a that iswide enough to allow a predetermined maximum angular pivoting while atthe same time being narrower than the component 12 d so that the plate11 acts as a guard rail to prevent the magnetic indicator from fallingoff the pivot 15. The way in which this location device works isillustrated in FIGS. 4 and 5.

To make it easier to detect the magnetic centre, the dome of themagnetic compass preferably has a detection means designed to determinewhether the axis X-X′ of the magnetic indicator is perpendicular to thereference plane Pr. In the embodiment illustrated, this means is acentering sight 19 positioned in such a way that the axis X-X′ of themagnetic indicator is in concordance with the axis Y-Y′ of the magneticcompass, perpendicular to the reference plane Pr, when the magneticcompass is superimposed on the valve and the magnetic indicator issituated precisely over the centre of the valve.

As illustrated in FIGS. 4 and 5, the user orientates the selector 20 ofthe device 100 according to the invention in such a way that thealignment mark 21 is aligned with the direction D in which the fluidflows through the valve. This direction D is determined at the time ofimplantation of the valve and remains constant throughout the patient'slife. The user also holds the device in such a way that the referenceplane Pr is parallel to the plane Pa formed by the magnets of the valve.The plane Pa is known and predetermined during implantation of the valvewhich, in general, is implanted in such a way that the plane Pa runssubstantially parallel to the surface of the skin, with an acceptabletrim error of a few degrees which may, for example, represent plus orminus 5°. It is therefore desirable for the device to be equipped with ameans of positioning with respect to the plane Pa. For example, theunderside 14 a of the housing 14 may be disposed parallel to the planePr so that all the user has to do is to position the device in such away that the underside 14 a is pressed against the patient's skin.

The user then moves the magnetic compass/selector assembly over thevalve, on the one hand maintaining the alignment of the device withrespect to the direction (D) in which the fluid flows through the valveand, on the other hand, keeping the reference plane Pr parallel to theplane Pa.

The user then immobilizes the magnetic compass/selector assembly whenthe magnetic indicator 12 is positioned substantially perpendicular tothe reference plane Pr, that is to say when the user notices that theaxis of the magnetic indicator 12 is positioned within the sight 19.

What happens is that the annular magnet 16 of the magnetic indicator 12aligns itself with the magnetic field generated by the magnets A₁-A₂ ofthe valve V, thus rotating the magnetic indicator about the pivot point.Thus, for all the time that the magnetic indicator 12 is not preciselysuperimposed on the magnetic centre of the valve V, it makes an angle awith the perpendicular to the reference plane Pr.

When the magnetic indicator 12 is positioned perpendicular to thereference plane Pr passing through the underside 14 a (FIGS. 5 and 10),that means that it is superimposed on the magnetic axis of the valve V,which means that the location of the magnetic centre of the valve V isknown accurately through the skin P.

There is therefore no need to have located the valve by palpationbeforehand in order to be able to locate its magnetic centre because themagnetic compass itself indicates the direction to follow. As a result,deeply implanted valves can be identified using the device according tothe invention. However, if the situation lends itself to such anapproach, that is to say when the valve is subcutaneous, and in order tosave time, the user may initially locate the valve V by palpation in theapproximate region in which the valve V is located before aligning theselector with the direction of flow D.

The valve setting is then represented by the angle β formed, in thereference plane, between the magnetic indicator 12 and the direction Dindicated by the alignment mark (FIG. 1), that is to say by the angle βformed between the orthogonal projection of the needle 12 a onto thereference plane Pr and the direction D. Thus, as illustrated in FIG. 1,it is possible on the interface 22 to read that the valve has been setto allow fluid to pass when the pressure is 110 mm H₂O (namely about1078.73 Pa) or higher.

The device can be contained in an assembly also equipped with a magneticfield emitter, known as a programmer, able to emit a magnetic fieldstrong enough to alter the setting of the valve. In such a case, havingaccurately located the magnetic centre of the valve and the valvesetting, the user commands the emission of a magnetic field strongenough to alter the setting of the valve. To do that, in the preferredembodiment in which the selector and the magnetic compass are separable,the user holds the selector 20 at the precise location where themagnetic centre of the valve has been located, removes the magneticcompass 10 from the selector 20 and replaces it) with a programmer ableto fit inside the selector 20. The user can then alter the settingappropriately according to the desired pressure setting for the valve.

FIGS. 7 and 8 illustrate another embodiment of a magnetic compass 40 ofa device for locating and indicating the setting of a magnetic valveaccording to the invention. In this embodiment, the magnetic indicatorconsists of a single component 42 having a part 42 a forming a needlethat indicates the setting, a part 42 b forming a pin, a part 42 d (FIG.8) for resting, and a part 42 f ₁-42 f ₂ for attaching two magnets 16 aand 16 b. A pivot reinforcing ruby 17 may also be positioned at theinterface between the pivot 15 and the part 42 d.

To assemble this magnetic compass (FIG. 7) it is necessary to choose aplate 11 that has a cut-out 11 b to allow the pin 42 b to be insertedinto the opening 11 a.

The other steps in the assembly are identical to that of the embodimentof FIG. 2.

FIG. 9 illustrates another embodiment combining the aforementioned twoembodiments, namely a one-piece magnetic indicator 52 comprising aneedle 52 a, a pin 52 b, a resting part 52 d located on an attachmentcomponent 52 e, and a part 52 f ₁-52 f ₂ for attaching the magnets 16 a,16 b.

The purpose of the part 52 e is to limit the maximum angle of pivotingof the magnetic indicator while at the same time limiting the amount ofruby to be used only at the pin/pivot contact point.

Furthermore, the magnetic indicator comprises a balancing ring 60improving the balance of the magnetic indicator 52 by counterbalancingthe weight of the attachment parts 52 f ₁ and 52 f ₂ between theseattachment parts.

This balancing ring 60 is positioned around the part 52 f ₁-52 f ₂ forattaching the magnet, coaxial with the pin 52 b and on the opposite sideof the part 52 d for resting on the pivot 15 to the setting-indicatingelement 52 a.

Furthermore, magnetic screening 18 intended to protect the magneticcompass from an external magnetic field other than that of the valve ispositioned around the magnetic indicator 52 and more specifically aroundthe magnets 16 a-16 b.

This screening can also be used in the aforementioned embodiments.

Numerous variations and alternatives may be adopted without therebydeparting from the invention. In particular:

-   -   the compass can be used to determine the setting of any type of        adjustable magnetic valve, such as the aforementioned        adjustable-pressure valves or adjustable-flow magnetic valves in        which the valve closes when a determined amount of fluid,        calculated as a function of the time for which the valve has        been open and of the set throughput, has passed through the        valve,    -   instead of being mounted resting on a rotation pivot, the        magnetic indicator may be mounted on a swivel or on three        respectively perpendicular pivot pins, so that the indicator can        position itself in all three dimensions in space;    -   the reference plane may consist of the base of the baseplate 14        rather than of an attached plate 11;    -   the detection means may be a sensor emitting an audible signal        when the axis of the magnetic indicator is perpendicular to the        reference plane;    -   the pivot-angle restrictor may have the form of a hemispherical        or hemiovoid swivel cage;    -   the magnet may be annular or may consist of two magnets;    -   the plate may be graduated to make it easier to read the valve        setting;    -   the reading interface 22 has as many setting-indicating marks 22        a as the valve has setting positions. Thus, in FIG. 1, the        reading interface is designed for a valve with up to five        setting positions. For a valve with, for example twenty-four        setting positions, the interface will have at least twenty-four        marks 22 a;    -   the magnetic indicator may comprise a visual means 23 of        indicating the mark 22 a that corresponds to the valve setting        position. This mark may be a simple symbol such as an arrow, a        coloured mark or a line, but may equally be embodied by a        particular shape of the magnetic indicator. This visual means is        especially useful when the marks 22 a are diametrically opposed        on the reading interface 22 because it makes it possible, from        two opposed marks 22 a, to determine unambiguously which is the        one that corresponds to the valve setting position.

The invention claimed is:
 1. A device for mechanically locating andreading the setting of an adjustable magnetic valve (v) for controllingthe flow of a fluid in a predetermined direction (D), comprising amagnetic compass (10) and a selector (20) provided with an alignmentmark (21) for aligning the magnetic compass (10) with respect to thedirection (D) in which the fluid flows through the valve (V),characterized in that the magnetic compass (10) comprises a referenceplane (Pr) and a magnetic indicator (12, 42, 52) which is mounted suchthat it can pivot in all three dimensions of space under the effect ofthe magnetic field of the valve, the valve setting being represented bythe angle (β) formed, in the reference plane, between the magneticindicator (12, 42, 52) and the alignment mark (21) when the magneticindicator (12, 42, 52) is positioned perpendicular to the referenceplane (Pr), the magnetic compass then being centered on the magneticcentre of the valve.
 2. A device according to claim 1, in which themagnetic compass has a detection means designed to determine whether theaxis (X-X′) of the magnetic indicator is perpendicular to the referenceplane (Pr).
 3. A device according to claim 2, in which a control meansis a centering sight (19).
 4. A device according to claim 1, in whichthe magnetic indicator (12, 42, 52) is designed to rest on a pivot (15)allowing it to rotate in all three dimensions of space under the effectof the magnetic field of the valve.
 5. A device according to claim 4, inwhich the magnetic indicator (12, 42, 52) has a pin (12 b, 42 b, 52 b)surmounted by a setting-indicating element (12 a, 42 a, 52 a) runningsubstantially perpendicular to the pin (12 b, 42 b, 52 b), a part (12 d,42 d, 52 d) for resting on the pivot and a part (12 f, 42 f 1-42 f 2, 52f) for attaching at least one magnet (16, 16 a, 16 b) able to receive amagnetic field.
 6. A device according to claim 5, in which the attachingpart (12 f, 42 f 1-42 f 2, 52 f) is disposed on the opposite side of theresting part (12 d, 42 d, 52 d) to the setting-indicating element (12 a,42 a, 52 a).
 7. A device according to claim 1, in which the magneticindicator (12, 42, 52) comprises a pivot-angle restrictor (12 e, 52 e).8. A device according to claim 7, in which the pivot-angle restrictor isin the form of a hemispherical, hemiovoid or frustoconical swivel cage.9. A device according to claim 5, in which a reinforcing means (17) ispositioned in the resting part (12 d, 42 d, 52 d) for the pivot (15).10. A device according to claim 9, in which the reinforcing means (17)is made of a material chosen from ruby, corundum and a ceramic.
 11. Adevice according to claim 5, in which a balancing ring (60) ispositioned around the part (12 f, 42 f 1-42 f 2, 52 f) for attaching themagnet (16, 16 a, 16 b) coaxial with the pin (12 b, 42 b, 52 b) and onthe opposite side of the part (12 d, 42 d, 52 d) for resting on thepivot (15) to the setting-indicating element (12 a, 42 a, 52 a).
 12. Adevice according to claim 1, further comprising magnetic screening (18)intended to protect the magnetic compass from an external magnetic fieldother than that of the valve.
 13. A device according to claim 1, inwhich the selector (20) and the magnetic compass (10) are separable. 14.A device according to claim 1, in which the selector (20) is equippedwith a reading interface (22) for reading the setting of the valve (V).15. An assembly for mechanically locating and reading the setting of anadjustable magnetic valve (V), comprising a device according to claim 1together with a programmer able to emit a magnetic field strong enoughto alter the setting of the valve.
 16. A method for mechanicallylocating and reading the setting of an adjustable magnetic valve forcontrolling the flow of a fluid with a device for indicating the settingof a valve according to claim 1, characterized in that it involves thesteps consisting in: a) orientating the selector (20) in such a way thatthe alignment mark (21) is aligned with the predetermined direction (D)in which the fluid flows through the valve; b) moving the said deviceover the valve, maintaining the alignment with respect to the direction(D) in which the fluid flows through the valve, c) immobilizing the saiddevice when the magnetic indicator (12, 42, 52) is positionedsubstantially perpendicular to the reference plane (Pr), then d)identifying the angle (β) formed, in the reference plane, between themagnetic indicator (12, 42, 52) and the direction (D) indicated by thealignment mark (21).
 17. A method according to claim 16, furthercomprising a step e) which consists in reading on a reading interface(22) a pressure value corresponding to the angle (β) identified in stepd).
 18. A method according to claim 16, further comprising a step f)which consists, in replacing the magnetic compass with a programmer ableto emit a magnetic field strong enough to alter a setting of the valveand emitting a magnetic field strong enough to alter the setting of thevalve.
 19. A method according to claim 16, further comprising apreliminary step which consists in initially locating the valve (V) bypalpation in an approximate region in which the valve is located.